> I am looking for help on determining recommended dimensions for thermal > vias and thermal via legs (spokes). I understand there is a trade-off > between making the vias large enough with small enough legs to allow the > board to be soldered without the use of a blast furnace versus making the > vias smaller with larger legs to allow for the required current capacity > of the connection. Any suggestions would be most appreciated. > > John Urry John, Why are you even considering "spoking" the vias? Vias are not related to a solderable component, requiring a solder process. We (I) have been doing spokeless plane layers for years now and have had absolutely! no complaints from countless fab houses on this design issue. My one recommendation though is to use a good size (say .020-.028" via size) for the thermal vias, and to have a thermal engineer give you a good formula for determining the amount of vias required. What I might also suggest is to open the soldermask around the thermal area (copper etch fills) and possibly even add thermal etch on the opposite side of the board (and open the soldermask from this area) for more thermal dissipation. Good Luck, Mitch Morey Cadence Design Supervisor Praegitzer Design San Diego, CA 92121 Phone: (619)450-0994 x-17 Pager: (619)982-7529 Fax: (619)450-0529 EMAIL: [log in to unmask] ||||| ((o o)) ____________________________oOO_(_)_OOo_____________________________ PCB layout is like fine art. You have to DIE to be famous! ____________________________________________________________________ (_) (_) *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************